uses_spec: Fix test for Linuxbrew on Travis
uses_spec: Fix test for Linuxbrew on Travis

When HOMEBREW_VERBOSE_USING_DOTS is set, as it is on Travis,
brew uses will produce output to stderr even when there's
nothing of interest there.

To make the tests pass, force this environment variable on
and then change the tests to expect this output.

Signed-off-by: Bob W. Hogg <c772a964fd55352a3510e5d535dd9ccc9ac30168@linux.com>

Linuxbrew/brew,rwhogg/brew,Linuxbrew/brew,maxim-belkin/brew,Linuxbrew/brew,rwhogg/brew,hanxue/linuxbrew,Linuxbrew/brew,rwhogg/brew,maxim-belkin/brew,hanxue/linuxbrew,hanxue/linuxbrew,maxim-belkin/brew